Modern semiconductor integrated circuit devices, or "chips," form their electrical connections with the outside world through pins. In particular, pins are used to supply power and ground reference potentials to the chip. For example, a CMOS or TTL semiconductor device receives a supply potential of 5 V through one pin, and a ground potential of 0 V through another pin. Integrated circuits implemented in other forms of logic, such as ECL, receive other reference potential levels as supply and ground and may even receive a plurality of supply potentials.
Pins are also used to carry electrical signals between chips. Specifically, pins provide electrical connections for transferring bit data from one chip to another. Conventional chips use multiple pins to input and output multiple bit data. For example, in FIG. 1, conventional IC 100 transmits 8-bit parallel data (a "byte") to IC 110 using transmit data pins D0 to D7 and transmit data strobe pin TDS. Transmit data strobe pin TDS is used for signalling that the multiple-bit data on pins D0 to D7 are valid. IC 110 receives the byte at pins D0 to D7, when signaled by received data strobe RDS. Pins D0 to D7 in FIG. 1 are bidirectional, allowing for data to be both transmitted and received through the same pins.
IC 100 further comprises receive data strobe pin RDS for receiving a signal indicating that data on pins D0 to D7 are ready to be read. In this configuration, the number of pins required for signalling is ten and the number of pins required for receiving reference potentials is two, for a total of twelve pins for each chip.
Pins, although necessary, consume space on the chip and often require expensive packaging. Therefore, a need exists to greatly reduce the number of pins required by semiconductor devices.